This invention relates to stream crossing structures, particularly natural bottom culverts and installation methods therefor that preserve the in-stream environment for fish to spawn, forage and migrate and that can withstand high water levels.
Roads are frequently constructed adjacent streams and, consequently, traversing the streams and their feeder streams often is necessary. This is particularly so in constructing logging roads in mountainous forest terrain. Prior to 1940, streams generally were crossed using either trestle bridges or puncheons (sometimes referred to as "Humboldt crossings"). While trestles were built above and across the streams, puncheons were constructed in the stream by laying large logs side-by-side longitudinally along the streambed, then laying additional logs across the stream transversing the first layer of logs and, finally, backfilling soil on top of the second layer to form the roadbed. So constructed, puncheons not only disturb the stream environment, but also have been subject to catastrophic failure. Nevertheless, puncheons allow fish to migrate because the bottom layer logs are spaced apart.
By the late 1940's, culverts were being widely used in place of puncheons to cross streams. Conventional culverts generally include round pipes or pipe arches with integral, solid bottoms. Culverts of this type are described, for example, in Shannon U.S. Pat. No. 1,071,185, Sivachenko U.S. Pat. No. 4,211,504, Peterson U.S. Pat. No. 4,563,107and Hwang U.S. Pat. No. 4,983,070. The artificial bottoms of such culverts impede the migration and spawning of fish, insects and crustaceans through the culvert because such culverts tend to move water at velocities above those natural to the stream while providing no place for the fish, insects and crustaceans to rest. Spawning, migration and foraging are further impeded because fish able to enter the culvert's exit cannot leave its upstream entrance if any impediment such as rocks, soil or other debris, is washed into that entrance. Moreover, damage results from water exiting the culvert at an elevated velocity, causing accelerated erosion of the soil and rock. While some conventional culverts are open at the bottom so as not to cover the entire natural streambed, as shown by Wolcott et al. U.S. Pat. No. 678,605, Pratt U.S. Pat. No. 597,590 and FitzSimons U.S. Pat. No. 4,558,969, their foundations tend to be undermined by the water. While attempts have been made to construct a culvert whose position cannot be changed by the water rushing through the culvert, this typically has resulted in a structure that necessarily disturbs the natural streambed as, for example, in Carswell et al. U.S. Pat. No. 1,955,407. Such structures tend to produce unnatural erosion of the streambed as well as corrosion caused by trapped debris.
Because both puncheons and conventional culverts have inherent shortcomings, a need exists for an improved stream crossing structure.